Method of operating an internal combustion engine and an internal combustion engine designed for carrying out this method

ABSTRACT

An internal combustion engine may be driven in the suction mode as well as the supercharging mode. Switchover from the suction to the supercharging mode takes place with the accelerator pedal in a switchover position, and switchback to the suction mode is effected in the return switching position of the accelerator pedal. The switchover and switchback positions are offset with respect to each other with the accelerator pedal in a central position between its initial position and its final position. The arrangement is such that the switchover position is reached at the end of the suction mode at fully open throttle flap (full power position). Upon switchover the throttling of the supercharging flow (throttling begin position) is increased as compared to the end of the suction mode. This throttling of the supercharging is diminished by further actuation of the accelerator pedal in the direction of the final position. Corresponding switchback from the supercharging to the suction mode takes place when the accelerator pedal is in the switchback position at which the drive of the supercharger established by the engine shaft is interrupted and a change is made from the stronger throttling during the supercharging mode to the weaker throttling in the suction mode.

This is a division of application Ser. No. 845,707, filed Mar. 27, 1986,now U.S. Pat. No. 4,730,593.

FIELD OF THE INVENTION

The invention relates to a method of operating an internal combustionengine and to the design of an internal combustion engine with a view torealizing this method.

BACKGROUND OF THE INVENTION

As is well known, the torque generated by an internal combustion engine,such as a 4-stroke engine has a maximum at a certain rotational speed ofthe engine and drops at increasing as well as decreasing numbers ofrevolution. The reduced torque in the range of low rotational speeds isdisadvantageous especially with motor vehicles because the accelerationis wanting.

Usually a change-speed gear including several transmission stages isprovided to displace the engine operation predominantly into arotational speed range in which the engine still provides a relativelyhigh torque. This useful measure which avoids overdimensioned pistondisplacement and the correspondingly high fuel consumption, however,solves the problem in part only because the number of transmissionstages must be limited in consideration alone of the frequency ofshifting. Consequently the problem remains of maintaining the mostuniform torque possible within a wider range of rotational speeds.

A known means for influencing the torque of an internal combustionengine, especially also the course of the torque as plotted over therotational speed of the engine, resides in supercharging the engine. Inthis case the boost takes care that an increased volume is supplied tothe combustion chambers as compared to the suction mode, and this leadsto increased performance without any increase in piston displacement. Asis well known, this may be influenced also by cam control and thus theduration of the supply phase and its position with respect to theignition time.

It is known to provide superchargers driven by the engine shaft, andthese may either be of the flow type (centrifugal compressors) or of thedisplacement type (vane cell compressor, Roots blower). Although thesemechanical superchargers driven by the engine shaft take up part of theengine output, they have the advantage over the known exhaust gasturbochargers of being able to become effective substantially withoutany delay in response.

Superchargers usually are driven at a much higher speed of rotation thanthe engine speed and this makes it necessary to provide a step-up gearbetween the engine shaft and the supercharger. It is also known withmechanical superchargers of the flow type to employ a gear of variabletransmission ratio controlled in response to the rotational speed, forinstance by means of a centrifugal governor. In this manner sufficientboost for the desired torque increase may be made available, especiallyat lower rotational speeds of the engine without requiring any wastefuldischarge of boost at higher engine speeds. A corresponding knownembodiment, therefore, may be regarded as being suitable in the firstplace to provide a convenient engine characteristic, especially inrespect of the course of the torque in consideration of the rotationalspeed of the engine without any increase in piston displacement and atlow fuel consumption.

It is known to connect a mechanically driven supercharger to the engineshaft by a magnetic clutch so that the supercharger may be switched onin addition rather than operating permanently together with the engine.Even in case of constant running together with the engine thesupercharger may be so designed or the boost so controlled by dischargethat the boosting effect substantially occurs at those engine speeds atwhich it is required. However this has the effect of deteriorating theefficiency or increasing the fuel consumption so that switching on ofthe supercharger, as required, appears to be advantageous.

With the known design including a magnetic clutch between the engine andthe supercharger, the supercharger is switched on by way of theaccelerator pedal after the latter has been pressed down during thesuction mode of the engine until the throttle flap has become fullyopen. This means that the suction mode is continued up to full power andthen an additional supercharging torque is made available by kick-down.However, this supercharging torque cannot be metered or applieddifferentiated in accordance with the respective rotational speed of theengine. This full switch of additional engine performance caused by thesupercharging is not entirely without difficulty. Especially the missingpossibility of metering has the effect that a motor vehicle travelling,for instance at full power in the suction mode at a velocity of 180 km/his accelerated by the torque applied additionally to a velocity of, forexample, 220 km/h because it is only at this point that the additionaltorque is used up by the additional road resistance caused by thevelocity. Therefore, it is not possible to travel at a constant velocityof, for instance, 200 km/h.

SUMMARY OF THE INVENTION

It is an object of the instant invention to operate an internalcombustion engine, especially a motor vehicle engine of the designmentioned initially and driven alternatingly in the suction andsupercharging modes such that harmless, smooth transition into thesupercharging mode is obtained and controllable in a mannercorresponding to the suction mode. It is another object of the instantinvention to achieve the above at low fuel consumption and simplestructure.

These objects are met, in accordance with the invention, in that theengine is driven in the suction mode only up to a central position ofits control member constituted, for example, by the accelerator pedal,that switchover is effected to the supercharging mode upon reaching ofthe central position of the control member, that the supercharging flowto the engine is throttled more upon switchover as compared to thethrottling at the end of the suction mode, and that further actuation ofthe control member beyond its central position opens the throttle crosssection for the supercharging flow, switchback from the superchargingmode to the suction mode being effected by return of the control member.

Observing these measures provides an additional torque by superchargingthe engine in response to the position of the control member oraccelerator pedal. This additional torque can be metered by more or lessstrong actuation of the control member upon reaching of the switchoverpoint. It is especially important in this context that the additionalsupercharging power does not become effective abruptly at the switchoverpoint because at first the supercharging pressure is largely kept awayfrom the engine by the stronger supercharging throttling as compared tothe suction throttling at the switchover point. It is obvious that thesupercharging throttling released by the switchover may be so designedthat the torque in supercharging operation beginning at the switchoverpoint is substantially the same as the torque generated at the end ofthe suction mode as the switchover point is reached. This has the effectof a smooth transition from the suction mode to the supercharging mode.Moreover, a limited, relatively small jump in output at the switchoverpoint causes no harm so that control of the supercharging throttling atthe switchover point allowing for all different operating conditions maybe dispensed with, if desired. Of course, the above statements applyaccordingly also to the switchback from the supercharging mode to thesuction mode where corresponding wide opening of the suction throttlingat the switchback point may be utilized in order to obtain more or lessaccurate adaptation of the suction performance beginning with thetransition into the suction mode to the final performance in thesupercharging mode upon reaching of the switchback point.

It is convenient to effect the switchback from the supercharging mode tothe suction mode at a control member position which is offset in thedirection of the initial position as compared to the control membercentral position which causes the switchover from the suction to thesupercharging mode. The offsetting of the switchover and switchbackpoints which differ by the opposed passing direction of the controlmember has the effect that a distinct mode of operation, namely suctionor supercharging is associated with each position of the control memberso that problems caused by uncontrolled multiple changes of theoperating mode at practically unvarying position of the control memberare excluded.

Thus it is proposed to effect the switchover from the suction mode tothe supercharging mode at a control member position within a range offrom 55% to 70% and the switchback from the supercharging mode to thesuction mode within a range of from 45% to 60% of the total path ofadjustment of the control member, based on the initial position thereof.These values at the same time provide an indication of the limits withinwhich the supercharger which consumes part of the engine output shouldbe switched on in order to fulfill the compromise between the desiredadaptation of the engine performance to the various operating states andlow fuel consumption, in other words to provide the best possibleefficiency.

An internal combustion engine corresponding to the above mentioned modeof operation and fulfilling the aim set starts from the known designmeasures according to which a supercharger of centrifugal compressortype adapted to be driven by the engine shaft through a rotational speedvariator having a transmission ratio controlled in response to therotational speed and connected to the engine shaft by a cutoff clutch,and a throttle flap are provided, the latter being disposed in theintake pipe to the engine and adapted to be shifted by a control memberfrom the closing position into a fully open operating position, thecutoff clutch being operable in response to the position of the controlmember.

In accordance with the invention the design is such that the throttleflap is adapted to be shifted into its fully open position by a firstpartial adjustment already of the control member from its initialposition into a central switchover position, that the cutoff clutch isoperable in the sense of engagement as the switchover position isreached, and that a supercharging throttle means is installed in thepipe connecting the supercharger with the engine and adapted to beopened to a final position by further partial adjustment of the controlmember from the switchover position, the return movement of the controlmember causing closing in corresponding manner, first of thesupercharging throttle means, and then of the throttle flap, upon havingreached a central switchback position at which the cutoff clutch isactuated in the disengaging sense.

An embodiment which allows for these features makes it possible tooperate the engine in the manner described above to correspond to thedifferent power requirements during engine operation, at relativelysmall piston displacement and consequently compact structure, while atthe same time keeping low the fuel consumption.

As regards the structural members required and their functions to befulfilled, there are no technical problems to overcome, all the more soas known control or regulating elements may be resorted to. Likewiseunnecessary are any members subject to much wear or high maintenancerequirements. A corresponding internal combustion engine including theaccessory equipment is suitable even for series manufacture because thecorresponding design does not involve any excessive capital investment,a circumstance favoring the use in the motor vehicle industry where theadvantages of the invention can be utilized primarily.

A convenient embodiment has the supercharger connected to the intakepipe and the supercharging throttle means formed by the throttle flapdisposed in the intake pipe and adjustable between the more open suctionposition and the more closed supercharging position by an adjustingmeans which is actuated as the switchover position is reached.

This embodiment proves to be of especially simple structure and requireshardly any additional space. For this reason this particular embodimentis suitable for retrofitting, especially motor vehicles already equippedwith a mechanical supercharger. In the interest of the simplest possibleinstallation, moreover it is possible alternatively to pass the suctionflow through the supercharger during the suction mode although thisleads to some throttling of the intake flow. Or a bypass pipe to thecompressor may be provided to be effective during the suction mode andbe made ineffective upon transition to the supercharging mode. Thisavoids circulation of the supercharging flow through the bypass pipewhich would reduce the efficiency.

In another convenient embodiment the supercharger is connected to theengine by a supercharging pipe comprising the supercharging throttlemeans and being separate from the intake pipe which includes thethrottle flap. In this case separate throttle members are provided forthe suction and supercharging modes and consequently they may remain intheir final positions upon switchover into the respective otheroperating mode (supercharging or suction modes). The final position thusat the same time constitutes the initial position for the renewedtransition to the respective other mode of operation. This may simplifythe throttling especially in the case of mechanical control.

If the intake and supercharging pipes are discharging in parallel intothe engine, of course, care must be taken that the respective pipe notused during one mode does not have any disturbing influence. This istrue particularly of the intake pipe during the supercharging mode. Forthis reason it is useful to associate a close-off means with the intakepipe to be operated as the switchover position is reached. Thisclose-off means, for example, may comprise a shutoff valve controlled bythe supercharging pressure prevailing downstream of the superchargingthrottle means.

Use may be made also within the limits of the invention of existingpossibilities of electronic control already applied with motor vehicleengines as well. Thus it is advantageous to provide the throttle flapand, if desired, also the separately provided supercharging throttlemeans with an adjusting motor and further to provide an electroniccontrol unit which receives positional signals from the control memberand controls the adjusting motor or motors as well as the cutoff clutch.The control unit may receive further signals characteristic of theengine operation, for example from a lambda probe installed in theexhaust gas pipe of the engine. Apart from controlling the throttling itmay control also the formation of the mixture or the injection of thefuel so that the engine may operate under optimum conditions wheneverpossible.

The switchover between the suction and supercharging modes effected inaccordance with the invention in response to the position of the controlmember corresponds best to the requirements normally existing duringdriving operation. However, there are special situations in which theautomatic passing over to the supercharging mode is less useful. If roadconditions are difficult and, especially on slippery roads because ofice or snow, too much tractive effort should be avoided if at allpossible. For this reason a convenient embodiment comprises a switchingmeans which includes an adjusting member adjustable between a positionfor the switchover between the suction and supercharging modes inresponse to the position of the control member and a switchoff positionat which the supercharger is switched off permanently. In this mannerproblematic road conditions can be allowed for by previous adjustment ofthe mode--mixed suction and supercharging or pure induction operation.

On the other hand, there are conditions under which it seems convenientto render the additional torque obtained by the supercharging availablesubstantially across the entire range of rotational speed of the engine.Such conditions are given, for instance, when driving over mountainpasses during which perfect metering of the torque is required in theentire torque range. Thus it is convenient also to provide a switchingmeans which includes an adjusting member adjustable between a positionfor switchover between the suction and supercharging modes in responseto the position of the control member and a constant superchargingposition at which the supercharger is driven permanently.

Of course, it is advantageous to combine in one switching means bothpossibilities, namely the complete switchoff of the supercharger and theconstant operation of the same. The adjustment member of this switchingmeans then would be adjustable selectively between the economic normalposition for mixed driving operation, the switchoff position for pureinduction operation, and the permanent supercharging position forconstant supercharging.

In the case of the embodiment for constant supercharging it isconvenient to associate a bypass pipe including a close-off means withthe supercharger and to subject it to the distributor pressuredownstream of the throttle flap such that the close-off means will openby low distributor pressure and cause circulation through thesupercharger and the bypass pipe accompanied by boost relief of thesupercharger. This design allows for the fact that during constantsupercharging, also with the throttle flap closed, such as during idlingand particularly in cases of thrust at higher rotational speed of theengine the supercharger would feed fully against the closed throttleflap and build up corresponding pressure, comparable to a pump. Such anoperating condition, if it lasted, could damage the supercharger,especially when driving downhill for prolonged times in the first orsecond gear in the thrust mode. This difficulty is effectively overcomeby the opening of the bypass pipe and the resulting relief of the boostcontrolled by the low distributor pressure.

The advantages of the invention may be utilized with any kind ofinternal combustion engine provided it is suitable for the suction andsupercharging modes. These may be injection engines or carburetorengines. A preferred field of application of the invention relates to4-stroke engines for installation into motor vehicles.

BRIEF DESCRIPTION OF THE DRAWING

Three embodiments of the invention will be described further withreference to the accompanying drawings, in which:

FIG. 1 shows an embodiment including a supercharger installed in theintake pipe and a single throttle flap operated by an adjusting motorfor the suction and supercharging modes of a carburetor engine;

FIG. 2 shows an embodiment including parallel intake and superchargingpipes with their own throttles operated by the accelerator pedal in aninjection engine;

FIG. 3 shows an embodiment without a separate supercharging pipe butwith a bypass pipe associated with the supercharger and a switchingmeans for the selective mixed mode, pure suction mode, and constantsupercharging mode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, an engine 1 is provided with four cylinders andincludes a drive shaft 2 for driving the wheels. A mixture distributor 3and an exhaust manifold 4 to which the exhaust pipe 5 is connected areassociated in per se known manner with the cylinders of the engine 1.

The intake pipe 6 opens into the mixture distributor 3, and asupercharger 7 of centrifugal compressor type followed by a throttle 8in the direction of flow and a flap 9 are installed in this pipe. Theflap 9 is adjustable by an adjusting motor 10.

To the input of the supercharger 7 or centrifugal compressor a conduit11 is connected which includes a carburetor 12 to the suction opening 13of which the fuel supply line is connected. An air filter 14 and a servoflap 15 adjustable by a servo adjusting motor 16 are disposed upstreamof the carburetor 12.

The supercharger 7 is driven by an engine shaft 17 which is connected toa rotational speed variator 18 embodied by a looping gear with which theeffective diameter of the driving and driven belt pulleys is adjustablein opposite sense and in response to the number of revolutions, forexample by centrifugal control. At its output end the rotational speedvariator 18 is connected by an electromagnetically operable cutoffclutch 19 to a transmission gear 20 which drives the rotor of thesupercharger 7 at higher rotational speed than the rotational speed ofthe engine shaft 17.

A control member in the form of an accelerator pedal 21 is associated inper se known manner with the engine 1. The respective position of thismember is entered into an electronic control unit 22 by a signal line.As shown in the drawing, a lambda probe 23 arranged in the exhaust pipe5 is connected by another signal line to the control unit 22 which inturn is connected to the adjusting motors 10 and 16 by further signallines for sensing or adjusting the same. Another signal line coming fromthe control unit 22 serves for actuation of the cutoff clutch 19.

The arrangement shown in FIG. 1 operates as follows: At the beginning ofthe engine operation the accelerator pedal 21 is in the initial positionA and flap 9 in its horizontal closing position S which is not shown inFIG. 1. The cutoff clutch 19 is disengaged so that the supercharger 7 isnot driven and the engine 1, when started, operates in the suction mode.This means that air is drawn in through the air filter 14 and a mixtureis formed in the carburetor 12 and flows through the supercharger 7 andthe intake pipe 6 to the engine 1 without any boosting effect. Pressingdown the pedal 21 will open the flap 9 by means of the control unit 22and the adjusting motor 10 so that the engine 1 will be poweredaccordingly. This induction operation is continued until the acceleratorpedal 21 reaches the switchover position U which is the position shownin the drawing for the gas pedal and at which the flap 9 has reached itsfully open vertical full power position V.

As the switchover position U is reached, the flap 9 at the same time ismoved back abruptly into the partly open throttling begin position LAshown in FIG. 1, and the cut-off clutch 19 is engaged so that thesupercharger 7 is driven by the engine shaft 17 and operation now is inthe supercharging mode. The additional torque made available by thesupercharging of for instance 1.4 bars, however, does not becomeeffective because the flap 9 has been moved back only into the partlyopen position LA at which the engine output in the supercharging modedoes not exceed the output supplied in the suction mode with the flap 9in full power position V, or exceeds the same only slightly. Therefore,the additional supercharger performance is released proportionally inresponse to the position of the flap 9 which is opened by furtheradjustment of the accelerator pedal 21 from the switchover position U tothe final position E from its supercharging begin position LA once moreinto the full power position V at which the maximum torque at therespective number of revolutions is obtained, in other words whendriving in the full power supercharging mode.

The switchback from the supercharging mode to the suction mode isreleased by the accelerator pedal 21 which, returning in the directiontoward the initial position A, reaches the switchback position R, acircumstance detected by the control unit 22. At this switchback pointthe cutoff clutch 19 is disengaged and flap 9 is again returned abruptlyfrom its position LA or a somewhat more closed flap position into thefull power position V. In this manner a continuous, smooth transitionwithout any noticeable jump in the output of the engine 1 takes placealso in passing over from the supercharging mode into the suction mode.

As shown in the drawing, the switchback position R is offset withrespect to the switchover position U in the direction of the initialposition A, whereby a distinct operating mode (suction or superchargingoperation) is associated with every position of the accelerator pedaland minute adjustments of the accelerator pedal 21 such as vibrations donot result in steady switching back and forth between the two operatingmodes. If, for instance, the path of adjustment of the accelerator pedal21 from the initial position A to the final position E is 100%, theswitchover position U may be provided in the area of 60% and theswitchback position R in the area of 50% of the adjusting distance fromA to E.

Moreover, it should be noted that the servo flap 15 is adjusted inconventional manner by the servo adjusting motor 16 from the controlunit 22 in order to influence the formation of the mixture in the mannerdesired.

The embodiment shown in FIG. 2 does not present a carburetor engine butinstead an injection engine 1. Besides, there is a great number ofsimilar or equivalent structural members which are marked by the samereference numerals as in FIG. 1 and thus will not be described again.

Other than in the case of FIG. 1, the supercharger 7 is built into asupercharging pipe 26 which is separate from the intake pipe 25 andprovided with its own supercharging throttle means 27 including a flap28. A close-off means 29 formed by a valve and a throttle flap 30following the same in the direction of flow are installed in the intakepipe 25. The close-off means 29 is biased into the closing positionshown by means of a weak spring 31. The pressure prevailing in themixture distributor 3 acts through a pressure sensor tube 32 on theclose-off means 29 such that low pressure in the distributor 3 willcause the close-off means 29 to overcome the pressure of the spring 31and move into open position. This assures that the intake pipe 25 isopen for flow in the suction mode, while it is blocked in thesupercharging mode when pressure is built up in the distributor 3.

An end switch 33 is coordinated with the throttle flap 30 and actuatedwhen the throttle flap 30 reaches the fully open position shown. Itpasses on the switching operation to a control unit 34 which actuatesthe cutoff clutch 19. The flap 28 and the throttle flap 30 are notactuated by means of the control unit 34 but instead directly from theaccelerator pedal 21 by mechanical links 35 and 36, respectively, asindicated. The presentation of the accelerator pedal 21 in FIG. 2corresponds to switchover position U in FIG. 1 at which the throttleflap 30 is in the fully open position corresponding to the full powerposition V, and flap 28 is partly open, corresponding to thesupercharging begin position LA. The links 35 and 36 are so designed andconnected to the accelerator pedal 21 that the pedal can be pressed downfurther into a final position whereby the flap 28 is opened until itreaches a fully open position, while the throttle flap 30 remains in thefully open position until the switchback position is reached by returnof the accelerator pedal 21. In this position the flap 28 will havereached the position shown or a somewhat more closed position and thethrottle flap 30 receives a first closing movement leading to renewedactuation of the end switch 33 and thus to the disengagement of thecut-off clutch 19.

As shown in the drawing, the intake pipe 25 and the supercharging pipe26 with the supercharger 7 are branched off in parallel from the conduit11 in which there is a central injection nozzle 37 and an air meter 38.In the area of the distributor 3 individual injection nozzles 39 areassociated with the individual cylinders.

Control unit 34 controls the injection of the fuel in response to theair meter 38 and the values measured by the lambda probe 23. Theinjection in the suction mode is effected through the individualinjection nozzles, whereas the injection nozzle 37 is used for centralinjection in the supercharging mode. In this event the downstreamsupercharger 7 driven by the engine shaft 17 warrants good turbulence orformation of the mixture.

The mode of operation of the arrangement shown in FIG. 2 corresponds tothat of the arrangement according to FIG. 1. However, because of theseparate flaps 28 and 30 for the supercharging and suction modes thesudden closing or opening of a flap at the points of switchover orswitchback does not occur. The mechanical coupling of the flaps 28 and30 with the accelerator pedal 21 also does away with flap control bymeans of the control unit 34. The embodiment shown in FIG. 3 relates toan injection engine 1 of largely similar design as the one shown in FIG.1 so that corresponding reference numerals were used again and thedescription below will be limited to the modifications given.

According to FIG. 3 the accelerator pedal 21 acts mechanically on theonly throttle flap 30 which closes the end switch 33 when almostentirely open. A switching means 40 including an adjusting member 41 isconnected to a storage battery 42, the end switch 33, and by a commonline to the cutoff clutch 19 and the central injection nozzle 37. Alsothe end switch 33 is in connection with this common line.

As shown in the drawing, the adjusting member 41 has three switchingpositions. In the position P (power) shown, it constantly connects thestorage battery with the cutoff clutch 19 so that the superchargeralways remains switched on, regardless of the position of theaccelerator pedal 21.

When the adjusting member 41 is in the position E (economy), the directconnection between the storage battery 42 and the cutoff clutch 19 isinterrupted and can be established only by the end switch 33. This isthe position for mixed operation at which the supercharger 7 is switchedon or off in response to the position of the accelerator pedal 21.

When adjusting member 41 is in the position O, the three contactterminals of the switching means 40 are separated so that the cutoffclutch 19 interrupts the driving connection between the engine shaft 17and the supercharger 7 and the engine 1 consequently operates in thesuction mode only.

A bypass pipe 43 is associated with the supercharger 7 to connect theconduit 11 with the intake pipe 6. A close-off means 29 and a spring 31are installed in the bypass pipe 43 and connected to the mixturedistributor 3 by a pressure sensor tube 32. This design and arrangementcorrespond substantially to what is shown in FIG. 2.

In the supercharging mode the supercharger 7 feeds pressurized airthrough the pipe 6 and the open throttle flap 30 to the mixturedistributor 3. Then the high pressure building up in the mixturedistributor 3 acts through the pressure sensor tube 32 to close theclose-off means 29 so that the supercharging operation is not affectedby the bypass pipe 43.

If the accelerator pedal 21 subsequently is taken back with theadjusting member 41 in position E, the end switch 33 is opened and thecurrent supply to the cutoff clutch 19 interrupted, whereby thesupercharger is turned off. Now low pressure will be developed in themixture distributor 3 and the close-off means 29 is opened against thepressure of spring 31. The engine 1 thus will draw in air through thebypass pipe 43 as well as through the supercharger 7.

In the supercharging mode and with substantially closed throttle flap30, an operating condition which may happen with the adjusting member inP position, the close-off means 29 opens under the effect of the lowpressure in the mixture distributor 3 which acts through the pressuresensor tube 32. This causes relief of the supercharger 7 and, at thesame time, a revolving flow takes place through the supercharger 7 andthe bypass pipe 43.

What is claimed is:
 1. In a method of operating an internal combustionengine, specifically an Otto engine for a power vehicle, which can runin a suction operation mode or in a supercharge operation mode by meansof a supercharger driven by said engine the method comprising the stepsof providing switchover means (21, 22 19; 21, 33, 34, 19) for switchingthe engine between a suction operation mode (A-U, R-A) and superchargeoperation mode (U-E, E-R) and providing at least one throttle flap (9;28, 30) and continually adjusting by said flap an engine torque in saidsuction operation mode and said supercharge operation mode, theimprovement comprising utilizing a centrifugal compressor as saidsupercharger, providing a speed variator (18) for driving saidsupercharger, and providing a supercharge pressure throttling relativeto said engine downstream of said supercharger in a supercharge line (6;26), wherein the supercharging flow to the engine is throttled more uponswitchover as compared to the throttling at the end of the suctionoperation mode, running said engine (1) in said suction operation mode(A-U) to a middle position (U) of a gas pedal (21), switching on thesupercharger (7) when said middle position is reached and therebyswitching to the supercharge operation mode (U-E) by operating the gaspedal (21) further over the middle position (U) to adjust said throttleflap (9; 28) for adjusting supercharge pressure, and by returning saidgas pedal causing switching-off said supercharger (7) to a middle gaspedal position (R) to switchover said engine to the suction operationmode (R-A).
 2. The method as defined in claim 1, wherein the enginetorque in the suction operation mode (A-U, R-A) and the superchargeoperation mode (U-E, E-R) is adjusted by the same throttle flap (9)which during the switchover to the supercharge operation mode (U-E) isset from an open suction position (V) to a more closed superchargeposition (LA) and during the switchover to the suction operation mode(R-A) is reset from the supercharge position to the more open suctionposition.
 3. The method as defined in claim 1, wherein the engine torquein the supercharge operation mode (U-E, E-R) and the suction operationmode (A-U, R-A) is adjusted by two different throttle flaps (28, 30)which during the switchover between two operation modes haverespectively different throttle angle positions.
 4. The method asdefined in claim 3, wherein the switchover from the superchargeoperation mode (E-R) to the suction operation mode (R-A) is obtained ata gas pedal position (R) which is shifted relative to the gas pedalposition (U) at the switchover from the suction operation mode (A-U) tothe supercharge operation mode (U-E) in the direction to the initialposition (A) of the gas pedal.
 5. The method as defined in claim 4,wherein the switchover from the suction operation mode (A-U) to thesupercharge operation mode (U-E) at a gas pedal position (U) is within arange 55% to 70% and the switchover from the supercharge operation mode(E-R) to the suction operation mode (R-A) at a gas pedal position (R) iswithin a range 45% to 60% of an entire adjustment path (A to E) of thegas pedal (21) from the initial position (A) thereof.
 6. A device foroperating an internal combustion engine, specifically an Otto engine fora power vehicle, which can run in a suction operation mode or in asupercharge operation mode by means of a supercharger driven by saidengine, the device comprising switchover means (21, 22, 19; 21, 33, 34,19) for switching the engine between a suction operation mode (A-U, R-A)and supercharge operation mode (U-E, E-R); at least one throttle flap(9; 28, 30) for continually adjusting an engine torque in said suctionoperation mode and said supercharge operation mode; said superchargerbeing formed by a centrifugal compressor; a speed variator (18) fordriving said supercharger; a supercharge line (6; 26), said throttleflap being positioned in said supercharge line, the engine having ashaft (17); said switchover means including said flap, a gas pedal and acutoff clutch (19) interconnected between said shaft and saidsupercharger (7), said throttle flap (9; 30) being adjustable by saidgas pedal (21) within the suction operation range (A-U, R-A) and withinthe supercharge operation range (U-E, E-R), wherein the arrangement issuch that the supercharging flow to the engine is throttled more uponswitchover as compared to the throttling at the end of the suctionoperation range.
 7. The device as defined in claim 6, wherein saidswitchover means (21, 22, 19; 21, 33, 34, 19) is actuated by the gaspedal in dependence upon a position (U, R) thereof.
 8. The device asdefined in claim 7, wherein a single throttle flap (9) in a singlesupercharge line (6) is provided for both operation modes; and furtherincluding at least one adjusting motor (10) connected to said throttleflap for adjusting said flap during switchover to the superchargeoperation mode from an open suction position (V) to a more closedsupercharge position (LA) and during switchover to the suction operationmode from a supercharge position to a more open suction position.
 9. Thedevice as defined in claim 7, further including a suction line (25) anda second throttle flap (30) positioned in said suction line, saidsuction line being separated from said supercharge line (26) with saidfirst one throttle flap (28), said first throttle flap and said secondthrottle flap being adjustable by the gas pedal (21) independently fromeach other within a respective operation mode range (U-E, E-R or A-U,R-A), the first throttle flap (28) being in a more closed position thanthe second throttle flap (30) when reaching the switchover positions (U,R).
 10. The device as defined in claim 9, further including close-offmeans (99) positioned in said suction line (25) and closing the suctionline upon switchover to the supercharge operation mode and opening saidsuction line upon switchover to said suction operation mode.
 11. Thedevice as defined in claim 6, wherein said close-off means (29) iscontrolled by supercharge pressure downstream of said first throttleflap (28) adjustable within the supercharge operation range (U-E, E-R).12. The device as defined in claim 6; further including an electroniccontrol device (22) which receives a signal from the gas pedal (21) andcontrols at least one adjusting motor (10) for said throttle flap (9)and said cutoff clutch.